Industrial reactions between reactant gases and liquids such as those involving hydrogenation of unsaturated organic compounds and those having functional groups capable of condensation are often performed by using finely divided powdered slurry catalysts in stirred-tank reactors. These slurry phase reaction systems are inherently problematic in chemical process safety, operability and productivity. The finely divided, powdered catalysts are often pyrophoric and require extensive operator handling during reactor charging and filtration. By the nature of their heat cycles for start-up and shut-down, slurry systems promote co-product formation which can shorten catalyst life and lower yield to the desired product.
An option to the use of finely divided powder catalysts in stirred reactors has been the use of pelleted catalysts in fixed bed reactors. While this reactor technology does eliminate much of the handling and waste problems, a number of engineering challenges have not permitted the application of fixed bed reactor technology to the reaction of gases with liquid organic compounds. Controlling the overall temperature rise and temperature gradients in the reaction process has been one problem. A second problem is that in fixed bed packed reactors there is a significant pressure drop due to the high flow rates required for hydrogenation. A third problem is that liquid-gas distribution is problematic thus often leading to poor conversion and localized concentration gradients.
Monolith catalytic reactors are an alternative to fixed bed reactors and have a number of advantages over conventional fixed bed reactors. These reactors have low pressure drop which allow them to be operated at higher gas and liquid velocities. These higher velocities of gas and liquids promote high mass transfer and mixing and the parallel channel design of a monolith inhibits the coalescence of the gas in the liquid phase.
The following patents and articles are illustrative of the prior art as they relate to gas/liquid reaction.
U.S. Pat. No. 5,763,687 discloses apparatus designed for the preparation of aromatic mononitro compounds. The reactor comprises a tube containing more than one twisted tabular member aligned in sequence, so that a front margin of one twisted tabular member is substantially perpendicular to a back margin of the preceding member. Preferably the reactor comprises a tube and a hollow tube without tabular members therein.
Patrick et al, AICHE Journal, Vol.41, No. 3 (March 1995) disclose a monolith reactor of uncoated cordierite and its use to determine residence time distribution and in designing gas/liquid phase reactions. Liquid and gas are introduced upflow through the monolith reactor with the reactant gas being passed through a porous glass frit. Gas bubbles generated by passage of gas through the glass frit are typically larger than the width of the monolith channels.
U.S. Pat. No. 6,005,143 relates to an improvement in a process for hydrogenating a nitroaromatic composition namely dinitrotoluene by contacting the dinitrotoluene with hydrogen in a reactor employing a monolith catalytic reactor system. Broadly the improvement resides in the continuous, essentially solventless, adiabatic hydrogenation of dinitrotoluene to toluenediamine in a monolith catalytic reactor operating in plug flow.
U.S. Pat. No. 4,428,922 discloses a method for manufacturing hydrogen peroxide in a fixed bed catalytic hydrogenator by utilizing a static mixer to premix hydrogen with the liquid prior to reaction in a fixed bed catalytic reactor.
U.S. Pat. No. 4,552,748 discloses a process for the production of hydrogen peroxide by passing a working solution and hydrogen upflow through a reactor comprised of parallel channels having a catalytically active material attached thereto. Reaction product is withdrawn from the upper portion of the reactor and recycled.
U.S. Pat. No. 5,688,047 discloses a static mixer with mixing elements. It is comprised of a tube and a mixing element rotated at an angle of 90° about the tube axis.